A method of freezing classified sperm cells compromised by a classification event, comprising the steps of: - obtaining a plurality of sperm cells； - subjecting said plurality of sperm cells to classification stresses； - selecting said plurality of sperm cells for a desired characteristic； - adding an egg yolk containing sperm cell extender to said plurality of sperm cells to form a first spread sperm cell mixture having a first protein content value； - cooling said first spread sperm cell mixture to a temperature less than 10 degrees Celsius to create a cooled first spread sperm cell mixture； - adding a sperm cell extender containing protein-free cryoprotectant having a volume equal to a volume of said first spread sperm cell mixture to said first chilled spread sperm cell mixture to form a second chilled spread sperm cell mixture having a second protein content value that includes more than 0.4 to 3.2 volume percent egg yolk； - keeping said second extended sperm cell mixture cooled in an unclear state； - centrifuging said second chilled extended sperm cell mixture； - add a supplemental protein-containing sperm cell extender to the second centrifuged chilled extended sperm cell mixture to increase the total protein content of such a protein-containing sperm cell extender having a third higher protein content value that the first value for protein content and that includes more than 1 to 50 percent by volume of egg yolk； -freezing said mixture of extended sperm cells.Un método para congelar células espermáticas clasificadas comprometidas por un evento de clasificación, que comprende las etapas de: - obtener una pluralidad de células espermáticas； - someter dicha pluralidad de células espermáticas a tensiones de clasificación； - seleccionar dicha pluralidad de células espermáticas para una característica deseada； - añadir un extendedor de células espermáticas que contienen yema de huevo a dicha pluralidad de células espermáticas para formar una primera mezcla de célu
